1. Field
This invention relates to network interfaces, more particularly to Integrated Services Digital Network (ISDN) interfaces.
2. Background
ISDN network architectures convey information from multiple networks to users. Typically, an ISDN transmits across two 64,000 bits per second (kbps) bearer, or B, channels, and one 16 kbps data, or D, channel. The D channel is used for signaling and control of the connection.
Various types of equipment maybe connected to the ISDN network through an interface. Users typically connect through various devices that are referred to as terminal equipment (TE). TE devices communicate to the network through network terminal (NT) equipment. NT equipment, also referred to as server-side, network-side, or network, interfaces may be between TE or other NT devices.
The two different interfaces, TE and NT, have specific characteristics with which they are associated. These characteristics are usually set out in Layers, using the term Layer as used in the Open System Interconnection (OSI) reference model. ISDN typically uses the first three layers. In the OSI reference model, layer 1 is the physical layer that manages putting data on the network and getting data off of the network. Layer 2 is the data link layer handling the physical passing of data. Layer 3 is the network layer, which routes data from one node to the other.
Typically, an interface identified as a TE interface will have specific characteristics of the physical and data link layers, such as synchronizing the clock from the connected line rather than sourcing its own. In addition, the network will view devices connected to this interface as a user-side device. This may cause a determination by the network as to what signals and messages can be sent to this particular device, because the network views it as user-side.
In addition, the TE layer 1 characteristics will include a clock synchronized from the connected line and no phantom power. Phantom power refers to a DC bias voltage provided on the line by NT interfaces, not provided by TE interfaces. These are just mentioned as an example, but become important factors when providing a network interface.
NT interfaces are currently assumed to have a network side layer 3. The network views them as a network interface, which in this instance means that the interface is between two network devices. NT interfaces typically have the characteristics of sourcing a clock and providing phantom power.
Currently, these interfaces are fairly rigid. Once an interface has been set up and configured, it is very difficult to change the characteristics without providing a new network interface board. These network interface boards are printed circuit boards, which are commonly referred to as network interface cards (NICs) or wide-area-network interface cards (WICs). In addition, the interfaces do not typically have separable layers. As mentioned above, if the physical layer is designated at TE, the network layer will be user-side. The clock will be synchronized from the interface and there will be no phantom power provided.
A user may have a legacy private branch exchange (PBX) that requires a user-side interface for layer 3. Currently, this interface would be designated as TE. If the user desires to have some of the additional signals and features that are available through NT interfaces, the user would have no method or means to obtain those. If the layers were separable, the user could designate the interface as NT and may gain access to some of those additional features and services, while meeting the requirement of having a user-side layer 3. However, this is not currently possible.
Some current interfaces allow a limited amount of flexibility. For example, the 6400 Vanguard™ Series from Motorola allows some configurability of network interface cards. However, the selectability is essentially only to select whether the interface is for TE or NT. Once that selection is made, there is no further flexibility. This does not solve the problems previously mentioned.
Therefore what is needed is a configurable interface that has separable layers.